The present invention relates to a magnet wire used in excitation coils in electrical equipment such as an electromagnetic relay, as well as to an electromagnetic relay using this magnet wire. In particular, the present invention relates to a magnet wire for use in a sealed type electromagnetic relay which has both relay contacts and drive coils confined and sealed in a common space. The present invention also relates to a sealed type electromagnetic relay using such a magnet wire.
Magnet wires of the type contemplated by the present invention are conventionally produced by the following procedures: a enamel of an electrically insulating material dissolved in an organic solvent is applied to the circumference of a conductor such as a copper wire and subsequently cured with heat to form an insulation coating, which is then coated with a layer of a lubricant such as paraffin or oil so as to provide good slipping property of the magnet wire and to prevent it from breaking during winding. Polyurethane based compounds are commonly used as the electrically insulating materials of the enamel. A cross section of the so prepared magnet wire is shown in FIG. 1, in which 1 is a conductor 2 is an insulation coating, and 3 is a layer of lubricant.
A sealed type electromagnetic relay using excitation coils which are formed of the magnet wire of the type described above is shown schematically in FIG. 2, in which the excitation coils are indicated by 4. As the relay is repeatedly operated, the lubricant component in the coils evaporate to generate a gas which fills the space in a closed vessel 5 and is deposited or carbonized by arc on the surface of contact elements 6 as it is cyclically brought into an open and a closed position. This deposition or carbonization of the evaporated lubricant component inevitably increases the contact resistance of the contact elements. In addition, the remaining solvent in the insulation coating of the coils 4, the unreacted phenolic compound used as a masking agent for the masked polyisocyanate which is one of the starting materials for the production of the polyurethane resin, and a low molecular weight organic compound such as the thermal decomposition product of the insulation coating which forms as a result of baking with heat, evaporate to generate a gas which fills the space in the vessel 5 and is carbonized on the surface of the contact elements 6 as it is cyclically brought into an open and a closed position, thereby increasing the contact resistance of the contact elements. In either case, the reliability of the sealed type electromagnetic relay is reduced.